I'd like to post my findings about phong alpha shader with an example of semi-transparent curtains.

Phong
alpha is only shader for which gray scale multiplier alpha layers can
be applied. We can use CAStable glass shaders for semi transparent
parts, but its transparency is defined by one parameter (simple
monotone).

Some objects such as bookshelves, dish washer, doll house, telephones, umbrella, etc. change their appearance depending on situations. For example, bookshelves change their appearance depending on how much books it contains.

By applying ‘Flat mirror’ shader to a group, you can easily have a
mirrored part (not functional) in your mesh. But the mirrored effect is
properly applied only to flat plane parallel to xy plane. You have to
adjust some parameters to make a mirrored plane which is not parallel to
xy plane.